Security Checklist/Where can you learn more about file permissions?
From Joomla! Documentation
Most current file systems today have methods of administering permissions or access rights to specific users and groups of users on computers. These permissions control the ability of the users to view and/or make changes to the contents of the files and/or the file directory(folder). To simplfy this explanation here, remember permissions are broken down by the following 3 designations in a Unix/Linux server:
r = Read permissions (the ability to view the file/files in a directory) w = Write permissions (the ability to write to the file/files in a directory) x = Execute permissions (the ability to execute the file/files in a directory)
The application of file permissions, directory permissions and their control depends on the operating system of the server and can be complex. Please read about the recommended permission settings for Joomla! or bad server permission settings.
Please read more about permissions and how to change them using the appropriate link to the correct server operating system or configuration:
Microsoft Windows based servers, the IIS(Internet Information Server) and PWS(Personal WebServer)